Spong, in a U.S. Application, Ser. No. 668,495 entitled, "Information Record and Related Recording and Playback Apparatus and Methods", now U.S. Pat. No. 4,097,895, issued June 27, 1978, has described an ablative recording medium which comprises a light reflective material, such as aluminum, which is coated with a thin film of an optically absorbing organic material, such as fluorescein. A focussed intensity modulated light beam, such as a laser beam from an argon or helium-cadmium laser, when directed at the recording medium, vaporizes or ablates the light absorbing material, leaving a hole or pit and exposing the reflective material. The thickness of the light absorbing layer is chosen so that the structure has minimum reflectivity. After recording there will be maximum contrast between the minimum reflectivity of the light absorbing layer and the higher reflectivity of the exposed metal material. Further, when the light reflective material is itself a thin layer on a nonconductive substrate, since little energy is lost through reflection from the thin absorbing layer, and little energy is lost by transmission through the reflecting layer, the energy absorption of the light beam is concentrated into a very thin film and recording sensitivity is surprisingly high.
U.S. Pat. No. 4,023,185 discloses that 4-phenylazo-1-naphthylamine provides an excellent light absorbing layer within the Spong structure which is absorptive at argon laser frequencies, and has improved toughness and abrasion resistance. This dye is applied by evaporation of Sudan Black B, which is thermally decomposed to form the naphthylamine layer.
Bloom et al, in a U.S. Application, Ser. No. 834,271, filed Sept. 19, 1977, entitled "Ablative Optical Recording Medium", have described a recording medium prepared by evaporating a light absorptive layer of di-indeno[1,2,3-cd:1', 2', 3'-lm]perylene over a light reflecting layer to form an antireflective layer at the recording wavelength. As taught in the copending Spong application, during recording, portions of the light absorptive layer are ablated by a modulated focussed light beam, thereby exposing portions of the reflecting layer. Thus, information is recorded as a reflective-antireflective pattern.
The above organic dye layers are somewhat soft and fragile and thus the dyes are desirably protected from dust and other airborne contaminants. Copending U.S. application of Bloom et al, "Thick Protective Overcoat Layer for Optical Video Disc", Ser. No. 828,815 filed Aug. 29, 1977, discloses applying a thick protective overcoat, such as a silicone resin, over the light absorptive layer. The information pattern is recorded through the protective overcoat which is comparatively undisturbed after recording. Only a few materials suitable for overcoat layers have been found because of the solubility of the above dyes in many organic polymer precursors. It would be desirable to find different dyes having good absorption at argon laser wavelengths.